Process for dehydrating tar



Jan. 9, 1945.

E. L. HALL ET AL PROCESS FOR DEHYDRATING TAR Filed June 27, 1940 2 sheets-sheet 1 a a 7"". x JM w wv. fw mwm \m\ J. s EMM@ LQW x QHUAH Jan. 9, 1945. E, L. HALL ETAL rRocEss FORDEHYDRATING TAR Filed June 27. 1940 2 Sheets-Sheet 2 mn naar mi i HINIMWIML Patented Jan. 9, i945 PROCESS FOR DEHYDRATING TAR Edwin L. Hall, Philadelphia, and Howard R. Batchelder, Drexel Hill, Pa., assignors to The United Gas Improvement Company, a corporation of Pennsylvania Application June 27, 1940, Serial No. 342,735

13 Claims.

This invention pertains to the recovery of valuable hydrocarbons from tar formed during the production of combustible gas by processes involving the pyrolytic decomposition of hydrocarbon oil, with or Without the aid of catalysts.

Various processes are known for the manufacture of combustible gas such as carburetted water gas and oil gas, wherein a petroleum oil such as crude oil or a fraction thereof, for example, gas oil or residuum oil, is pyrolytically decomposed.

In such processes the gas leaving the gas-making apparatus is usually brought into contact with Water such as inthe Wash-box, and as a result the tar which separates from the gas is usually recovered in the form of an emulsion with Water. Thus the tar emulsion in extreme cases may contain as high as 95% Water or even higher. In some cases the tar emulsion may be in the form of a pasty solid of very high viscosity. As a rule, the tar emulsion will contain at least 50% water and in this respect diiiers from tars obtained in processes for the production of coal gas or coke oven gas, or in many oil cracking processes for the production of motor fuel, for in the latter processes the tar as recovered is not in an emulsion form. Therefore, the terms tar emulsion or petroleum tar emulsion as used hereinafter and in the claims refer to emulsions of tar and water produced in the manner described; namely, during the manufacture of combustible gas by processes involving the pyrolytic decomposition of petroleum oil.

The recovered mixture of tar and water from gas-making operations involving the decomposition of petroleum oil is usually :tirst collected in a settling tank for the separation of as much water as possible by layer formation and decantation.

In accordance with prior art practice the relatively stable tar emulsion which remains after separation of the Water layer is usually treated according to some method of dehydration such as centrifuging or distillation.

Centrifugal methods of treating tar emulsions, however, separate only the tar and the water of the emulsion and do not separate lighter vtar constituents from the heavier. Furthermore, the presence of free carbon in the emulsion may give rise to operating di'lculties.

The separation of the tar emulsion by distillation results in fractions which comprise (l) Water, (2) a distillate from the tar comprising light oil and dead oil, and (3) residual tar.

For purposes of convenience in description,

that portion of the distillate boiling up to approximately 200 C. (392 F.) at atmospheric pressure will be designated light oil and'that portion of the distillate boiling above approxi'- mately 200 C. (392 F.) at atmospheric pressure will be designated dead oil. These may be separated by distillation.

The light oil fraction contains, among other things, valuable saturated and unsaturated aromatic hydrocarbons such as benzene, toluene, xylene, styrene, methyl styrene, indene, etc.

'Ihe dead oil fraction contains naphthalene, methyl and other substituted naphthalenes, and may contain anthracene, methyl anthracene, as well as numerous other hydrocarbons for the most part as yet unidentified.

The residual tar still contains polymerizable constituents.

The residual tar has a number of uses. For example, it may be used as a road tar, or as a heavy liquid fuel. For both purposes the control of the viscosity of the residual tar is of importance because of its eiect upon the ease of handling.

Due to the fact that the tar is subjected to elevated temperatures for considerable lengths of time in ordinary distillation procedures of the prior art for breaking the emulsion and for the separation of light oil and dead oil as distillate,

substantial polymerization is caused to take place. Such polymerization tends to reduce the quantity of distillate on the one hand because heat polymerizable constituents Which are vaporizable in monomeric form are polymerized, and to increase the viscosity of the residual tar on the other, both of which are undesirable.

These disadvantages are eiectively overcome in the practice of our invention.

In accordance with our invention, tar emulsions may be dehydrated in a manner (1) such that the yield of dead oil therefrom may be increased at the expense of residual tar Without encountering a corresponding increase in viscosity of the residual tar; or (2) such that for a given yield of dead oil, a residual tar of lower viscosity ris obtainable than by conventional methods. Furthermore, it is possible to obtain by our process a higher dead oil yield than is possible by conventional methods because it is possible to take overhead heat polymerizable constituents in monomeric form, which constituents in the prior art are polymerized part of theresidual tar.

Residual tar viscosityv is of importance in the art. For example, an increase in tar viscosity results. in an increase in handling diiilculty.

and become a With our invention, more dead loil may be re- :overed for any given selected residual tar vis- :osity than by conventional methods for tar deiydration in use at the present time.

Further features of the invention will become Lpparent to those skilled in the art as the specioation proceeds.

In the practice of our invention a tar emul-v not remain at operating temperatures for protracted periods. Thus; polymerization is materially reduced with the result that a larger proportion of the tar itself including heat polymerizable constituents boiling in the dead oil range may be taken E overhead as distillate along with the water While processing the bottom of residual material to any given residual tar viscosity.

It will be understood that two factors aiect residual tar viscosity, namely (l) the proportion of relatively iluid oils left in the residual tar which may be controlled by the proportion of volatile material removed overhead, and (2) the proportion of unsaturated material polymerize'd into less volatile, more viscous polymers. In our process assuming that other things remain unchanged, item l preceding may be increased and decreased by decrease and increase in the temperature to which the original tar is subjected. However, consideration should be given to the effect of higher temperatures upon item 2 preceding taken in conjunction with heating time. Since polymerization is a function of both temperature and time, the effect of higher temperatures during shorter heating times may be made the equivalent of the eiect of lower temperatures during longer heating times. We nd, however, that a relatively wide range of both temperature and heating time is aiorded particularly when operatingat sub-atmospheric pressures, without losing the advantage over conventional methods of tar dehydration, although we prefer to maintain item 2 preceding at a virtual minimum or at least relatively low.

Our invention may be more particularly described in connection with the accompanying drawings in which:

Figure 1 is a flow sheet illustrating one embodiment of the invention; and

Figure 2 is a now sheet illustrating another embodiment of the invention. i

Referring now to Figure 1, tar-water emulsion is introduced by pipe 2 and pump 4 into a heater E in which its temperature is raised appropriately and from which the heated material ows through pipe 8 into separating zone or chamber The more volatile materials contained in the tar emulsion including water, light oil and dead oil are vaporized in heater and the heated mass is projected into chamber l0.

Chamber l is designed to facilitate the rapid separation of the vaporized and unvaporized portions, For example, it may be relatively empty.

The vaporized portion rises to the top of chamber id, flows through line l5 to condenser i8 from cooled. Removal of residual tar may be accomplished either continuously or intermittently, for

example, by the use of a hand operated or autov matically operated valve appropriately associated withY the bottom of chamber I0, or a level-operated pump, or a submerged pump in a well, each being preferably operated to avoid a considerable accumulation -of tar in chamber l0.

As illustrated the residual tar is removed automatically and continuously through a liquid seal formed by the tar itself.v

No particular form of apparatus is critical for this purpose, although we nd that some forms are more satisfactory than others. One form which is very satisfactory is indicated diagrammatically at the bottom of chamber l0.

The base-of separating chamber I0 is shown reduced in diameter thus forming well 40 which is connected to the main body of the chamber I0 by a sloping frusto-conical wall 42.

An inner pipe 44 passes through and rises from the bottom of the well 40 to create an annular zone 45. An inverted cup 46 is disposed above and around pipe 44 and as shown extends downwardly into annular zone 45.

Residual tar dropping to the bottom of chamber I0 enters annular zone 45 about the outside of cup 46, flows down around and into the inside of the cup, and overflows the top ol" riser 44 from which it flows through pipe 48 into residual tar cooler 50 in which the residual tar is preferably cooled suiciently to substantially reduce or prevent any further polymerization. The residual tar flows from cooler 50 through pipe 52 to any suitable point such as to storage.

Since the liquid seal holds only a small amount of residual tar which is constantly washed away and out of chamber l0 by the newly formed residual tar, it will be seen that no portion of the residual tar after separation is held at elevated temperatures for an extended period of time.

While the flow of residual tar from chamber l0 is preferably continuous, it may be continual or intermittent if desired, for any reason. Thus, we have shown a valve 49 in pipe 48 to facilitate such continual or intermittent withdrawal, should such be desired for any reason.

Returning now to the settling tank 24, the function of which is primarily to separate the various layers which form from the condensate, it is found that an emulsion layer indicated generally at 25 sometimes forms between the hydrocarbon distillate layer indicated at 26 and ,the water layer indicated at 21.

Accordingly, settling tank 24 is illustrated with three outlets, 28, 29 and 30 for draining-off emulsion, hydrocarbon distillate and water, respectively.

The hydrocarbon distillate may be further processed such as by fractionation to produce desired -hydrocarbon fractions. For example, it might be initially separated into light oil and dead oil.

The water may be discarded or utilized in some manner, if desired.

The emulsion, if any, may be further treated to recover its hydrocarbon content. Thus, the emulsion may be passed through a lter bed capable of breaking the same, of which filter beds made of sand, lead wool, steel Wool, etc., are examples. On the other hand, this emulsion might be recycled through heater 8 and chamber I0* It is found that the ratio of emulsion (if any) to hydrocarbon distillate and water may vary considerably With operating conditions and the character ofthe tar undergoing treatment.

It is also found that the tendency of the hydrocarbon distillate and water to form emulsion-s may be very substantially reduced, if not eliminated, by fractionally condensing from the vapors leaving chamber I a, part or all of the relatively higher boiling hydrocarbons, leaving substantially all of the water and the rest of the hydrocarbon distillate to be condensed in condenser I8 and separated in settling tank 24. This partial condensation washes from the overhead vapors any nely divided solid or semi-solid matter such as finely divided carbon particles which are apparently responsible for the formation of emulsions when they occur. Other steps may be employed for removing these particles should they occur in the vapors. Thus chamber I0 may be designed or operated in such a manner as t0 avoid carrying overhead emulsion-forming materials.

Any desired means may be employed for condensing out relatively high boiling hydrocarbons from the vapors iiowing from separating chamber I8, For example, a. partial condenser 3| is illustrated in line I6 between condenser I8 and chamber IU.

High boiling hydrocarbons condensed in condenser 3| may be drained ol through outlet 32 controlled by valve 33 into cooler 38.

Other things remaining equal, the temperature to which a given tar emulsion is heated in heater 6 will depend upon the'desired ratio of hydrocarbon distillate to residual tar, it being understood that the higher the temperature the higher the ratio of hydrocarbon distillate to residual tar and the higher the residual tar viscosity.

It is found that as a general rule, with other things remaining the same, including the temperature of heating, the ratio -of hydrocarbon distillate to residual tar increases with increase in the percentage of water in the tar emulsion. It follows that for any given ratio of hydrocarbon distillate t0 residual tar the final temperature reached in heater 6 decreases with increase in percentage of water in the tar emulsion undergoing treatment.

p Ihe phenomenon is quite apparently connected with the reduction in partial pressure of the hydrocarbon distillate vapor as a result of the presence of steam generated from the water in the tar emulsion.

Accordingly, should it be desired to further decrease the partial pressure of the vapors of the hydrocarbon distillate in any case and thus, for example, take a larger proportion of hydrocarbon distillate oi overhead, or the same proportion at Va lower temperature, steam might be added at an appropriate point such as at 35 at the bottom of chamber I0 or at 36 at the inlet to heater 6, or at 31 at the outlet of heater 6, or at any other appropriate point or points.

It will, of course, be understood that water itself might be added at 36 since it would be vaporized to steam in passing through heater 6.

The partial pressure of hydrocarbon distillate vapors may also be reduced by reducing the pressure in chamber I0, as already referred t above. This may be conveniently accomplished by attaching pressure regulating mechanism, for exl ample, a vacuum pump, to outlet 20 of condenser I8, proper steps being taken to effectively drain condensate into settling tank 24, for instance, by inserting a vacuum leg in line 22 or connecting settling tank 24 to vacuum.

Since polymerization is a function not only of temperature but also of time, we prefer to bring the tar emulsion undergoing treatment to the desired temperature in heater ii as rapidly as practicable and then immediately discharge it into chamber I8 for separation of its components.

It is also preferred to have at least the preponderant part of the vaporization take place in heater 6 so as to abstract at least the preponderant part of the necessary heat of vaporization directly from heater 8. In other words, it is preferred to operatesuch that dashing of liquid to vapor in the separating chamber l0 occurs, if at all, only to a relatively minor extent, or at most is only incidental to the preponderant vaporization in heater 6. Y

Since for any given temperature in heater 6. other things remaining unchanged, the amount of vaporization will decrease with increase in pressure, it is preferred to choose or design heater 6 so as to have a relatively small pressure drop between the point at which the materials undergoing treatment reach the maximum temperature and the point at which they are projected into the chamber |0 This is to permit the preponderant part of the Vaporization to take place within the heater itself. The total pressure drop across the heater will depend. upon its design and operation and keeping in mind what has just been said, it may have any desired or convenient value high or low.

However, should it be desired for any reason, higher pressures might be employed.

If desired, extraneous heat may be. added to chamber I8, for example, by adding superheated steam at 35 at a temperature above theaverage temperature of chamber I0. Another means of adding heat to chamber Il) is by the insertion of a steam or other heating coil therein. Other means for adding heat to chamber I0, if desired, will occur` to persons skilled in the art upon becoming familiar herewith.

Generally speaking, however, we usually prefer to restrict any. heating of chamber I0 to compensate for unavoidable heat losses.

The following examples will serve to further illustrate the invention. l

Example 1 A tar emulsion containing water was processed in a small pilot plant corresponding in general to Figure 1 of the drawings. The separating ing distillation to theA same residual tar viscosity yielded (neglecting the water) only 45% distillate,v

and 55% tar residue.

, l EzampZeZ Another tar emulsion containing 68% water l was processed in the same manner a's in Example Example 3 Another tar emulsion of a somewhat different character and containing 65% water was processed in the same manner as in Example 1, the pressure in the separating chamber being maintained at approximately 50 mm. of mercury. The temperature of the materials undergoing treatment at the outlet of the heater was maintained at approximately 268 F.

55% of the tar (neglecting the water) was recovered as distillate and 45% as residue.

'I'he viscosity of the tar residue in SSF 210 F. was 530.

Another sample of the same'tar emulsion processed conventionally to the same tar viscosity yielded (neglecting the water) only 39% distillate, and 61% tar residue.

The foregoing examples amply demonstrate the advantages of our process over the conventional processes of the prior art.

A separation of the hydrocarbon distillate obtained in our process into light oil and dead oil fractions shows that the large increase in hydrocarbon distillate by the practice of our process is for the major part, if not preponderantly, in dead oil.

In other words, the outstanding advantages of our process reside in the recovery of much larger percentages of dead oil than have heretofore been possible, and without disadvantageously affecting the recovery of light oil either quantitatively or qualitatively.

Thus, measurably'larger quantities of dead oil are recovered without polymerizing significant quantities of the polymerizable unsaturates in the light oil fraction.

While theA tar emulsion may be brought to any merization, it is preferred to use temperatures between approximately 200 and 350 F.

Likewise while any desired pressure may be maintained in chamber I0, it is preferred to operate at pressures below atmospheric. Thus the use of temperatures between approximately 200o and 350 F. in conjunction with pressures between approximately 20 and 200 mm. of mercury (absolute) is found particularly effective.

While the time interval during Which a tar particle is subjected to polymerizing temperatures in passing through heater E and separating chamber I0 and until it is finally cooled, may vary considerably without sacrificing the advantages of our process, we prefer that this-time interval be short; or in other Words, that the transit of each tar particle be rapid through zones of sufficiently high temperature to cause polymerization.

Heater 6, chamber I0 and tar seal l0 lend themselves conveniently to designs by which the holdup of materials in process may be maintained relatively small, thus lending themselves to .a rapid transit of tar particles through that portion of the process in which they are subjected to polymerizing temperatures.

The apparatus is preferably so designed and operated that the time interval during which the average tar particle is subjected to temperatures higher than about F. beginning in heater 6 and ending in condenser I8 or cooler 34 or cooler 50 does not exceed 30 minutes, with 5 to l5 minutes as a better gure.

When the highest temperatures do not greatly exceed 200 F., this time interval may be extended somewhat, and when they approach or exceed 350 F., it is preferablyshorter.

Accordingly, condenser I8 and coolers 34 and 50 are preferably operated at temperatures below about 120 F. As an example, they may be operated at atmospheric temperature or somewhat above or below, using river water' as a cooling medium.

It will be understood of course that the numerous and complex variables involved make it difficult to calculate the time interval just referred to with absolute accuracy. As exemplifying some of these variables may be mentioned the variations in constituency of the tar emulsions, the extremely complex nature of the hydrocarbon components thereof, differences in the physical characteristics of the tar emulsions, the extreme sensitivity to heat of certain constituents thereof, etc.

However, it ispossible by making certain simplifying assumptions to derive empirically an expression for the time interval of exposure of tar to elevated temperatures, which expression will serve for practicable purposes in performing the process and will form a valid basis for comparing results obtained.

Thus, for example, it will be helpful to assume that (a) the composition of the tar emulsion `is 50% water, 30% oil (light oil plus dead oil), and 20% residual tar; (b) the density of the tar emulsion is 62.5 lbs. per cu. ft.; (c) the increase in volume due to vaporization and/or change in temperature and pressure occurs uniformly throughout the heater, so that'the average volume through the heater is one-half the sum of the inlet and outlet volumes; (d) the average molecular weight of the volatilized hydrocarbon material is (e) the density of the residual tar at operating temperature is 62.5 lbs. per cu. ft.; and (f) the operation conditions are at an average temperature of 250 F. in the heater and a pressure of 2 lbs. per sq. in. absolute (i. e., about -100 mm. of mercury) in the separating chamber.

From this it can be shown that the volume of materials entering the heater is negligible in comparison with the volume of the materials leaving the heater. Hence, the average volume of materials through the heater can be taken as one-half-of that leaving the heater without introducing any appreciable error.

Furthermore, for the purpose of calculating the said time interval the volume of the tar distillate vapors and of the unvaporiz'ed residual tar can normally be neglected. This is because (1) the volume of residual tar is relatively small in comparison to the vaporized material, and (2) the molecular weight of water is so low compared to theaverage molecular weights of the vaporized hydrocarbons that in the mass leaving heater 5 steam is present in the order of 92% or more by volume. The calculations for the heater proper, therefore, may be made, without introducing too large an error, on the basis of the water content of the tar emulsion.

Stated generally therefore in terms of a throughput of W lbs. of water per hour, a heater temperature of TR (Rankine) an absolute pressure in the separating chamber of P lbs. per square inch, and a heater volume of Vn cubic feet, the time of exposure in the heater in hours equals:

Vh average volume of Waterthrou gh the heater per hour Vh V1.1 %W T 14.7 0.3WT i5 X359 -P If the tar well of the separating chamber has a volume in cubic feet of Vtw, and the yield of residual tar in pounds per hour is Rt, then the time of exposure in the tar well is represented by Vm, 62.5V,w residual tar per hour (cubic feet) R,

Since the time of exposure of any particular Dart of the hydrocarbon vapor to temperatures above 120 F. after leaving heater 6 is less than that for liquid residual tar particles because of the speed with which the Vapor travels to oondenser I8, the approximate average total time interval (in minutes) in the entire apparatus may, therefore, conveniently be expressed as If the point in the heater at which the materials reach 120 F. is determined at least approximately, and the volume of the heater substituted in the above formula is taken as from that point instead of from the inlet, the formula gives an approximation of the average time interval during which the materials in process are maintained at a temperature above 120 F.

As previously mentioned, the apparatus is preferably so designed and operated that the value 3f this expression rarely exceeds 30, with 15 as a better figure and 5 as excellent.

It will, of course, be understood that apparatus for carrying out the invention may be of any desired design, construction or shape suitable for the purpose.

Thus while chamber l has been shown empty, my other suitable interior structure may be rdopted consistent with its function as a separating chamber. I

Likewise, heater 6 may take any form or shape ind may be of any type suitable for the purpose. As an example, a pipe still may be employed rlthough a shell-and-tube heater might also be :onveniently employed. The heater 6 is preferibly so designed as to insure the discharge of )oth liquid and vapor into separating chamber I0, for example, by resorting to the self-draining irinciple for the liquid, or to suiiciently high 'apor velocities to carry the liquid along with yhe vapor, or both, or otherwise. This is, of purse, to avoid the separation and polymerizaion of tar in the heater 6 with resulting stopiages.

Likewise, condensers i8 and 3l, coolers 3B and 0 and settling tank 2t may be of any desiredv :onstruction suitable for their respective purioses.

While the invention has been more particularly lescribed in connection with a single vaporization tep, it is to be understood that vaporization may perature is raised appropriately, for example,-

between 190 and 230 F., and from which the heated material flows through pipe 64 into separating zone orv chamber 65 which may be maintained at any suitable pressure such as atmospheric.

The lighter portions of the volatile materials contained in the tar emulsion, including a substantial part of the light oil and some of the water, are vaporized in heater 63 and the heated mass is projected into chamber 65.

The vaporized portion is taken olf through line EB to condenser 61 from which the condensate flows through line 68 to settling tank 69 and from which any uncondensed or ,uncondensable gas flows olf through line 'lll for further condensation or other treatment, or otherwise, as desired.

The unvaporized portion which still contains at least a substantial part of the dead oil and the rest of the water falls to the bottom of chamber 65 and is preferably rapidly removed therefrom with a relatively small, if any, hold-up for the same reasons as given in the particular description of Figure 1 in connection with the removal of residual tar from chamber l0. Accordingly, and for convenience, chamber B5 is illustrated as having the same construction as chamber l0.

The unvaporized material flows off through pipe ll to pump l2 and then into heater 13 in which its temperature is raised appropriately such as between 200 F. and 350 F., and from which the heated material flows through pipe 'lil into separating zone or chamber 'l5 which may be maintained at any suitable pressure such as between 20 and 200 mm. of mercury, absolute.

The rest of the volatile materials which it is desired to remove from the tar'and the rest of the water are vaporized in heater i3 and the heated mass is projected into chamber l5.

The vaporized portion flows oi through line 76 to condenser 'l from which the condensate flows through line '1S to settling tank T9 and from which any uncondensed or uncondensable gas ows off through line 80 for further condensation or other treatment, or otherwise, as desired.

The portion left unvaporized in heater 13 and chamber l5 comprises the residual tar which falls to the bottom of chamber '15, and as in the case of the vaporized portion it is preferably rapidly removed from chamber 15 and cooled.

Accordingly, and for convenience, chamber l5 has been illustrated as of the same construction as chambers l0 and 65, although lt Will be understood that these chambers need not have the same construction and that any other suitable construction might be substituted.

As shown, residual tar flows off through pipe 8| into residual tar cooler 82 in which the residual trated with two outlets 84 and 85 for draining ofi! light hydrocarbon distillate and water respectively.

The function of settling tank 19 is also to separate the various layers which. formfrom the condensate and since an emulsion layer might be formed, depending of course upon the design and operation of separating chamber 15, the settling tank 19 is illustrated with three outlets 86, 81 and 88 for draining off emulsion, hydrocarbon distillate and water, respectively.

It is, of course, to be understood that any tendency for an emulsion to form may be reduced or prevented the samel as already described in connection with Figure 1, namely by placing a partial condenser in line 16, or by the design and/or operation of separating chamber 155, or both, or otherwise.

It is also to be understood that such emulsion, if any. may be treated to recover its hydrocarbon content the same as already described in connection with Figure 1.

The heavy hydrocarbon distillate has been illustrated in settling tank 19 for convenience as the top layer. Its density is very close to that of water and changes more rapidly with temperature. Accordingly, it is found that the heavy hydrocarbon distillate might comprise the lower layer When temperatures in settling tank 19 are somewhat 10W.

If desired, steam might be added to either the rst or the second vaporization steps, or both, at any appropriate point or points, for example, as illustrated in Figure 1.

The same applies to the addition of supplementary heat to chambers 65 and 15.

In practice it is found that steam will be used more often in connection with the second separation step than in the first, although when the percentage of hydrocarbon distillate taken off in the first step is relatively high,'some steam might be desired.

Chambers B5 and l5 may be operated at any desired pressure which may be conveniently regulated at l and 00 respectively, such as by venting to the atmosphere or by using pressure regulating mechanism.

Thus, chambers G and i5 might be operated at atmospheric, super-atmospheric or sub-atmospheric pressures, although atmospheric and subatmospheric pressures will usually be employed.

As an example, chamber may be operated at atmospheric pressure and chamber l5 at subatmospheric pressure.

Thus for example, when the collection of the larger part of the light oil lis in settling tank (i9 and the larger part of the dead oil is in settling tank l0, chamber 05 may be operated at substantially atmospheric pressure and the temperature of the incoming materials undergoing separation may be between 190 and 230 F.; and chamber iii may be operated at a pressure between 20 and 200 mm. of mercury and the temperature of the incoming materials may be between 200 and 350 F.

Other combinations of temperatures and press sures will suggest themselves to persons skilled in the art upon becoming familiar herewith.

As in the case of Figure l, the time interval during which the average tar particle is subjected to temperatures higher than 120 F. preferably does not exceed 30 minutes with 15 minutes as a better figure and 5 minutes as excellent, these times being determined by the formula set forth herein. Also as in the case of lFigure 1 when the highest temperatures do not greatly exceed 200 F., the time interval may be extended and when they approach or exceed the 350 F., it is preferably shorter. However, as previously stated although We prefer the time interval to be short it may vary considerably without sacriiicing the advantages of our process.

A two or more stage process is particularly recommended in cases where the tar emulsion contains relatively high percentages of light materials suchas benzene, since the rst stage permits such materials to be condensed at a higher pressure than might be desired in the second stage, particularly if it is desired to take a considerable quantity of' high boiling material oil overhead in the second stage. y

For example, to condense vaporsrhaving a relatively high benzene content at pressures of the order of 20 mm. of mercury might require temperatures suiiiciently low to solidify benzene ir the condenser after it is liqueed. Thus, taking on benzene at higher pressures such as atmospheric has distinct advantages when the benzene `content of the tar emulsion is relatively high.v

On the other hand, duplicate condensers mighi be provided and used alternately, with one thawing while the other is in use, should. solidiflcation diiiiculties be encountered. Other means foi overcoming any such difficulties, should they occur, will become apparent to persons skilled ir the art upon becoming familiar herewith.

Apparatus for a three or more stage treatmeni will become apparent to persons skilled in thi are upon becoming familiar With the foregoing Many other variations may be made.

For the purposes of the claims expressions o1 units of time, where occurring, are to be construed as being calculated by the empirical formula set forth herein, or its equivalent. However in the case of variations, modifications o: the formula may be employed if required.

It is to be understood that the foregoing i: by way of illustration and that changes, omissions, additions, substitutions and/or modifica 'tions might be made within the scope of thi claims without departing from the spirit of the invention.

With respect to products produced by the process described herein reference is made to our copending application Serial Number 370,008, file: December 18, 1940.

We claim:

1. A process for the dehydration of a petroleun tar emulsion with the simultaneous separation o the constituents of the tar into hydrocarbon distillate and tar residue with decreased polymerization, comprising rapidly heating said ta: emulsion to a temperature sufficiently high an( under a pressure sufficiently low to vaporise z substantial portion of the constituents oi the ta: boiling above 392 F. at atmospheric pressure rapidly separating the vaporized and unvapo rized portions, and then rapidly cooling the separated portions of the tar to below polymerizin; temperatures.

2. A process for the dehydration of a petroleum tar emulsion with the simultaneous separatioi oi the constituents of the tar into hydrocarboi distillate and tar residue with decreased poly merlzation, comprising rapidly heating said ta` emulsion to a temperature suliciently high an: under a pressure suiiic'iently low to vaporize it more volatile constituents including a substan tial portionv boiling above 392 F. at atmospheril pressure, rapidly separating the resulting vapo rized and unvaporized portions, and rapidly cooling the separate portions of the tar to below polymerizing temperature, said process being conducted such that the average time during which tar particles are subjected to temperatures above 120 F. does not exceed 30 minutes.

3. A process for dehydrating a petroleum tar I emulsion produced in the manufacture of combustible gas wherein petroleum oil is pyrolvticcily decomposed. said tar emulsion containing a substantial amount of water, comprising heating a rapidly moving mass of said tar emulsion under reduced pressure to a temperature between 200 and 350 F. thereby transforming a substantial portion of the hydrocarbon content of said tar emulsion boiling above 392 F. at atmospheric pressure from liquid-phase to vapor-phase within the rapidly moving mass, projecting the heated tar emulsion Without large pressure drop into a separation zone maintained at a reduced pressure between 20 and 200 mm. Hg for the rapid separation of vaporized and unvaporized portions, rapidly withdrawing the vaporized portion as overhead from the separating zone, rapidly withdrawing the unvaporized portion as residual tar from the separating zone, and cooling the portions thus withdrawn to below polymerizing temperatures.

4. A process for the dehydration of apetroleum tar emulsion with the simultaneous separation of the constituents of the tar into hydrocarbon distillate and tar residue with decreased polymerization, comprising rapidly and successively heating said tar emulsion suiciently with intermediate separation of vapors-to vaporize more volatile constituents including a substantial portion boiling above 392 F. at atmospheric pressure, making a final separation of vaporized and unvaporized portions. and rapidly cooling said separated vaporized and unvaporized portions to below polymerizing temperatures.

5. A multi-stage process for dehydrating a petroleum tar emulsion produced in the manufacture of combustible gas by the pyrolytic decomposition of petroleum oil which comprises rapidly heating said tar emulsion in a continuous stream to a temperature between 190 and 230 F., said temperature being suiciently high to vaporize a large part of said tar emulsion boiling below 392 F. at atmospheric pressure, projecting the heated tar emulsion without large pressure drop into a separation zone maintained at substantially atmospheric pressure for the rapid separation of vaporized and unvaporized portions, rapidly removing said vaporized and unvaporized portions from said separation zone, rapidly cooling the vaporized portion to below polymerizing temperatures, immediately heating the removed unvaporized portion in a continuous stream to a temperature between 200 and 350 F., said temperture being suiciently high to vaporize a substantial portion of the remaining volatile hydrocarbon content of said tar boiling above 392 F. at atmospheric pressure, projecting said last mentioned heated portion without large pressure drop into a separation zone maintained at a pressure between 20 and 200 mm. Hg for the rabid separation of vaporized and unvaporized portions rapidly removing said last mentioned vaporized and unvaporized portionsl from said last mentioned separation zone, and cooling said last; mentioned portions to below polymerizing temperatures. I

6. In a process for the dehydration of a petroleum tar-water emulsion with the separation of the constituents of the tar into hydrocarbon distillate and tar residue, said tar containing heat polymerizable constituents boiling above 392 F. when at atmospheric pressure, the steps of rapidly vaporizing water and tar constituents contained in a rapidly flowing stream of said petroleum tar-water emulsion, and separating the resulting vaporized and unvaporized portions, said vaporization being conducted at a temperature sutciently high to vaporize a considerable portion of the constituents of said tar which boil above 392 F. when at atmospheric pressure, and said vaporization and separation being conducted .suiiiciently rapidly to separate in heat polymeifizable form and as a part of said vaporized portion a considerable portion of said heat polymerizable constituents boiling above 392 F. when at atmospheric pressure.

7. In a process for the dehydration of a petroleum tar-water emulsion with the separation of the constituents of the tar into hydrocarbon distillate and tar residue with decreased polymerization of heat sensitive constituents of the tar which boil above 392 F. at atmospheric pressure, the steps of heating a rapidly moving stream of petroleum tar-water emulsion to a temperature sufliciently high to vaporize a considerable portion of the constituents of the tar which boil above 392 F. when at atmospheric pressure, projecting said heated stream into a separating Zone and therein rapidly separating the resulting vaporized portion including water, light oil and dead oil constituents from the unvaporized portion including tar residue, said vaporization and separation being effected with suicient rapidity to recover from the tar in heat polymerizable form a considerable portion of said heat sensitive constituents boiling above 392 F. When'at atmospheric pressure as a part of said separated vaporized portion.

8. In a process for the dehydration of a petroleum tar-water emulsion with the separation of the constituents of the tar into hydrocarbon distillate and tar residue with decreased polymerization of heat sensitive constituents of the tar which boil above 392 F. when at atmospheric pressure, the steps of rapidly iiowing a stream of petroleum tar-water emulsion through a heating zone and heating said stream therein to a temperature suilciently high to vaporize a considerable portion of the constituents of said emulsion which boil below 392 F. when at atmospheric pressure, releasing the heated stream in a separating zone and therein rapidly separating the resulting vaporized constituents from unvaporized constituents, rapidly owing a stream of said separated unvaporized constituents through a second heating zone for heating therein to a temperature suiiiciently high to vaporize a considerable portion of the previously unvaporized constituents boiling above 392 F. when at atmospheric pressure, releasing the heated stream resulting from said second heating step in a second separating zone and therein separating the resulting vaporized constituents from unvaporized constituents, said vaporization and separation steps being cont ducted suiiiciently rapidly to recover from the tar as separated vaporized heat polymerizable constituents a considerable portion of the heat sensitive constituents of the tar which boil above 392 F. when at atmospheric pressure.

' 9. In a process for the dehydration of a petroleum tar-water emulsion with the separation of the constituents of the tar into hydrocarbon distillate and tar residue with decreased polymerization of heat sensitive constituents of the tar which boil above 392 F. when at atmospheric pressure, the steps of rapidly owing a stream of petroleum tar-water emulsionthrough a heating zone and heating said stream therein to a tempera- ,ture suiciently high under the pressure conditions obtaining to vaporize a considerable portion of the constituents of said emulsion whichboil below 392 F. when at atmospheric pressure, discharging the heated stream into a separating zone maintained at substantially atmospheric pressure and therein rapidly separating the resulting vaporized constituents from unvaporiz'edv constituents, rapidly flowing a stream of said separated unvapo-rized constituents through a second heating zone and heating said stream therein to a temperature sufficiently high under the pressure conditions obtaining to vaporize a considerable portion of the previously unvaporized constituents boiling above 392 F. when at atmospheric pressure, discharging the heated stream resulting from said second heating step into a second separating zone maintained at a reduced pressure between approximately 20 mm. and 200 mm. of mercury and therein separating the resulting vaporized constituents from unvaporized constituents, said Vaporization and separation steps being conducted suiciently rapidly to recover from the tar as separated vaporized heat `polymerizable constituents a considerable portion of the heat sensitive constituents of the tar which boil above 392 F. when at atmospheric. pressure.

l0. In a process for the dehydration of a petroleum tar-water emulsion with the separation of the constituents of the tar into hydrocarbon distillate and tar residue with decreased polymerization of heat sensitive constituents of the tar which boil above 392 F. when at atmospheric pressure, the steps of rapidly iiowing a stream of petroleum tar-water emulsion through a heating zone and heating said stream therein under temperature conditions sufficiently high under the pressure conditions obtaining to vaporize a considerable portion of the constituents of said emulsion which boil below 392 F. when at atmospheric pressure, discharging the heated stream without large pressure drop into a separating zone maintained at approximately atmospheric pressure and therein rapidly separating the resulting vaporized constituents frornlunvaporized constituents, rapidly iiowing astream of said separated unvaporized constituents through a second heating zone and heating said streams therein under temperature conditions between approximately 200 and 350 F. and sufficiently high under the pressure conditions obtaining to vaporize a considerable portion of the previously unvaporized constituents boiling above 392 F. when at atmospheric pressure, discharging the heated stream resulting from said second heating step without large pressure drop into a second separating Zone maintained at reduced pressure between approximately 20 mm. and 200 mm. of mercury and therein separating the resulting vaporized constituents from unvaporized constituents, said vaporizations being eiected preponderantly in said heating Zones as distinguished from said separating zones, and said vaporization and separation steps being conducted sufficiently rapidly to recover from the tar as separated vaporized heat polymerizable constituents a considerable portion of the heat sensitive constituents of the tar which boil above 392 F, when at atmospheric pressure.

l1. In a process for the dehydration of a petroleum tar-water emulsion with the separation of the constituents of the tar into hydrocarbon distillate and tar residue with decreased polymerization of -heat sensitive constituents of the tar which boil above 392 F. when at atmospheric pressure, the steps of heating a rapidly moving stream of petroleum tar-water emulsion in a heating zone to a temperature suiciently, high under the pressure conditions obtaining to vaporize a considerable Vportion ofthe constituents .of the tar which boil above 392 F. when at atmospheric pressure, discharging said heated stream without, large pressure drop into a separating zone, and therein rapidly separating the resulting vaporized portion from the unvaporized portion, the preponderant part of said vaporization taking place in said heating zone as distinguished from said separating zone, and said vaporization and separation being eiected with sufiicient rapidity to recover from the tar in heat polymer-izable form a considerable portion of said heat sensitive constituents boiling above ,392 when at atmospheic pressure as a part of said separated vaporize'd portion.

12. In a process for the dehydration of a petroleum tar-water emulsion with the separation of the constituents of the tar intov hydrocarbony distillate and tar residue with decreased polymerization of heat sensitive constituents ofthe tar which boil above 392 F. when vat atmospheric pressure, said petroleum tar-water emulsion having been previously treated to reduce its content of material boiling below 392 F. when at atmospheric pressure, the steps of heating a rapidly moving stream o f petroleum tar-water emulsion in a heating zone to a temperature between approximately 200 and 350 F. and suiciently high under the pressure conditions obtaining to vaporize a considerable portion of the constituents of the tar which boil above 392 F. when at atmospheric pressure, discharging said heated stream without large pressure drop into a separating zone maintained at reduced pressure'between approximately 20 mm. and 200 rnrn. of mercury and therein rapidly separating'the resulting vaporized portion from the ,unvaporized portion, the preponderant part'of said vaporization taking place in said heating zone as distinguished from said separating zone, vand said vaporization and separation being effected with surhcient rapidity to recover from the tar in heat polymeriaable form a considerable portion of said heat sensitive constituents boiling above 392 F. when at atmospheric pressure as a part of said separated vaporized portion, Y

13, In a process for the dehydration of a. petroleum tar-water emulsion with the separation of the constituents of the tar into hydrocarbon distillate and tar residue with decreased polymeilzation of heat sensitive constituents of the tar which boil above 392 F, when at atmospheric pressure, the steps or rapidly flowing a stream of petroleum tar-water emulsion through a heating zone and heating said stream therein under temperature conditions sufficiently high under the pressure conditions obtaining to Vaporize a considerable portion of the constituents of sa'id emulsion which boil below 392 F. when at atmospheric pressure, discharging the heated stream without large pressure drop into a separating zone maintained at approximately atmospheric pressure and therein rapidly separatl ing the resulting vaporized constituents from unvaporized constituents, rapidly owing a stream of said separated unvaporizedv constituents through a second heating Zone and heating said stream therein in the presence of additional steam and under temperature conditions sufoiently high under the pressure conditions obtaining to vaporze a considerable portion of the previously unvaporized constituents boiling above 392 F. when at atmospheric pressure, discharging the heated stream resulting from said second heating step without large pressure drop into a second separating zone maintained at reduced pressure and therein separating the resulting va porized constituents from unvaporized constituents, said vaporizations being eected preponderantly in said heating zones as distinguished from said separating zones, and said vaporization and separation steps being conducted sufticiently rapidly to recover from the tar as separated vaporized heat polymerizable constituents a considerable portion of the heat sensitive constituents of the tar which boil above 392 F. when at atmospheric pressure.

EDWIN L. HALL.

HOWARD R. BATCI'm'LDER. 

